The present invention is related to optical coating equipment and, more particularly, to systems for depositing optical coatings on optical substrates at very precise and controlled thicknesses.
Many optical elements are typically covered with thin-film optical coatings to either increase the transmissivity or the reflectivity of light through the elements to increase the performance of the elements. Even the lenses of most eyeglasses have optical coatings for better visibility. From the nature of light, the thickness of the coatings should be precise and uniform.
Optical coating systems rely upon a variety of techniques, such as sputtering (e.g., rf), and evaporation (e.g., resistance heating, e-beam, rf inductive heating) depending upon the requirements of the coating process. Where high volume production is required, the coating system can operate with a technique suitable for a large number of substrates. Where precision is required, the system operates with a technique by which the coating process can be carefully controlled and reliably duplicated. Heretofore, as one might expect, optical coating systems with high volume capabilities have not been capable of high precision, nor has the reverse been true.
One optical element which requires extremely precise and controlled optical coatings is the multicoated narrow bandpass filter suitable for the WDM (Wavelength Division Multiplexing) network, or the newer Dense WDM (Dense Wavelength Division Multiplexing) network. In such fiberoptic networks, the wavelength of a light signal directs the signal from a source toward one or more destinations. By the DWDM network standard, communication channels have a wavelength separation of only 0.8 nm (or a frequency separation of 100 GHz). Hence a wavelength filter must be extremely discriminating. For a narrow bandpass filter formed by multiple coatings on a substrate, the manufacturing requirements are quite severe. Such filters typically have coatings from 85-125 layers, with minimal variations in thickness distribution for each layer. As expected, the cost of these elements is quite high, well over one hundred U.S. dollars per filter element at the present. For a fiberoptic network having hundreds, if not thousands, of WDM coupler devices, each having such a filter as a component, the costs of these coupler devices alone become very high. Hence it is desirable that the costs of manufacturing precision coated optical elements, such as narrow bandpass filters, Rugate filters, dichroic filters and the like, be lowered.
Toward this end, the present invention is directed toward improved precision optical coating systems and methods of operation, which are capable of production at volumes much higher than found heretofore. Furthermore, the present invention also provides the improvements in the control and precision in the deposition of the optical coatings for improved optical performances by the resulting optical elements.